There are several applications in which an operating mechanism is connected to a remotely located device by means of a Bowden cable. One example of such an application is a steering column mounted lever for selecting forward and reverse gear in a tractor. In this case, the opposite end of the Bowden cable would be a mechanical control lever on the gearbox or to a remotely located hydraulic selector valve. It is important in such an application that the lever movement should be positive, i.e. with minimal free play, so as to provide a firm feel to the operator.
EP 0 560 645 discloses a gear lever mechanism remotely connected to a gearbox by two Bowden cables, one for transmitting the left to right movements in the neutral position of the gear lever and the other for transmitting the front and rear movements that engage the different gear ratios. To transmit the left to right movement in the neutral position, an actuating arm is secured to the gear lever in such manner that it rotates with the gear lever during left to right movements but rotates about a transverse pin relative to the gear lever during front and rear movements. The free end of the actuating arm is coupled to one arm of a bellcrank lever of which the other arm is connected to one of the Bowden cables.
The coupling between the actuating arm and the bellcrank lever comprises a sliding ball and socket joint. Such a joint, in addition to allowing the relative inclination of the actuating arm and the bellcrank lever arm to change, allows the distance between them to vary. This is implemented in EP 0 564 645 by a pin that projects from the bellcrank lever and extends parallel to its axis of rotation. The pin carries at its end a ball that slidably engages in a cylindrical socket mounted on the actuating arm. In this construction, the sliding axis of the joint is the axis of the cylinder in which the ball is received.
Because the sliding axis in EP 0 564 645 extends parallel to the axis of the bellcrank lever, the coupling only works because, as earlier mentioned, the actuating arm is pivotable relative to the gear lever and can therefore move towards and away from the pivot point of the bellcrank lever as it rotates. In the absence of such an additional degree of motion of the actuating arm, the coupling between the actuating arm and the bellcrank lever would lock in one position.
The requirement for an additional pivot makes the cable operating mechanism more bulky and complex, and there is a need for more moving parts that are all prone to wear.